Trump’s favorite diplomatic tactic is to suck up to strongmen. No previous American president in my lifetime has done it to the same degree that he does. Why?
Because he looks at Xi and Putin and Sisi and Kim and Erdogan and the rest of the gang and sees himself. He knows that he demands that everyone around him fawn over him. That’s the way he decides to dole out favors. Why should the others be different? The world is nothing more than a stage for a handful of great men; if you can build a good personal relationship with them, everything falls into place.
Unfortunately for him, the world doesn’t actually work that way, and the strongmen in question are neither as stupid nor as susceptible to flattery as he is. That’s why his efforts at diplomacy don’t work.